void main()
{
	int i,n,s=0,a[10],b[10];
	double c[10],g=0;
	scanf("%d",&n);
	for(i=0;i<n;i++){
		scanf("%d",&a[i]);
		s+=a[i];
	}
	for(i=0;i<n;i++){
		scanf("%d",&b[i]);
		if(b[i]>=90&&b[i]<=100){
			c[i]=4.0;
		}
		if(b[i]>=85&&b[i]<=89){
			c[i]=3.7;
		}
		if(b[i]>=82&&b[i]<=84){
			c[i]=3.3;
		}
		if(b[i]>=77&&b[i]<=81){
			c[i]=3.0;
		}
		if(b[i]>=75&&b[i]<=77){
			c[i]=2.7;
		}
		if(b[i]>=72&&b[i]<=74){
			c[i]=2.3;
		}
		if(b[i]>=68&&b[i]<=71){
			c[i]=2.0;
		}
		if(b[i]>=64&&b[i]<=67){
			c[i]=1.5;
		}
		if(b[i]>=60&&b[i]<=63){
			c[i]=1.0;
		}
		if(b[i]>=0&&b[i]<=59){
			c[i]=0;
		}
	}
	for(i=0;i<n;i++){
		g+=c[i]*a[i];
	}
	printf("%.2lf\n",g/s);
}